Current distributor



April 5, 1949.

R G. HOOF CURRENT DISTRIBUTOR Filed June 15, 1947 .629 50 5 5w" 506 A50 5 A 3.. L :2. if?

INVENTOR ROBERT G. HOOF ATTORNEY Patented Apr. 5, 1949 CURRENT DISTRIBUTOR Robert G. Hoof, Glendale, CaliL, assignor to Bendix Aviation Corporation, a corporation of Delaware Application June 13, 1947, Serial No. 754,511

1 Claim.

This invention relates to electrical switching systems for successively connecting a source of current to a plurality of circuits, and will be described as applied ts the electrical deicing of airplane propellers.

An object of the invention is to provide a current distributor that is simple, reliable and remains in accurately timed condition indefinitely so that there is negligible pause and no overlap between the breaking of the current flow to one circuit and instigation of the current flow to the next circuit.

Other more specific objects and features of the invention will appear from the detailed description to iollow of certain embodiments thereof.

In the deicing of airplane propellers by electric heating elements built therein, it is more effective to apply a heavy current for a short time than a lighter current for a proportionately longer time. However, the total current capacity available on an airplane is usually insufi'icient to supply a heavy current to all the propellers simultaneously, or in some instances even to all the blades of a single propeller simultaneously. It has therefore been customary to employ some form of motordriven switch for successively switching all the heating current to difierent propellers or propeller blades. In the case of an airplane having four, 4-blade propellers, in which the current is concentrated in one pair of opposite blades of one propeller at a time, distribution must be made to eight different circuits.

Heretotore, the distributors used have either been of the commutator type or of the cam-actuated-contact type, both of which have serious disadvantages. The commutator type does not require adjustment, but is expensive and short-* lived because of arcing. The cam-actuated-contact type is long-lived, but is undesirable because of the difliculty of making and maintaining the adjustment of the contacts so that they make and break at the right instants.

The present invention eliminates the mentioned defects of the prior systems by employing a combination or commutator type switches and cam-actuated switches. In accordance with the invention, the commutator type switches successively prepare paths to the diflerent heating pellers;

circuit in overlapping relation, and the circuits are completed by cam actuation 01' a double throw switch, which simultaneously breaks one of the paths created by the commutator switch and completes the other path. When the cam-actu- 'ated, double throw switch is next actuated, the I commutator-type switch will have prepared a new Fig. 2 is a schematic diagram showing an application of the invention to the distribution of heating current to four 3-blade propellers;

Fig. 3 is a sectional view illustrating one type of switch unit that can be employed in practising the invention, the view being taken in the plane III III of Fig, 4;

Fig. 4 is a section taken in the plane IV--IV of Fig. 3; and

Fig. 5 is a graph illustrating the operation 01 the systems of Figs. 1 and 2.

Referring first to Fig. 1, there are shown four propellers l5, l6, l1, and I8, each having four blades 20. Each of the blades 20 contains an 8180! trical heating element It for deicing the blade.

One terminal or each heating element It is connected to ground. The other terminals of each pair of heating elements in each pair of opposite blades 20 of the propeller are connected together and to a common relay contact. Thus the two heating elements lta in one pair of opposite blades 20 01' the propeller I! are connected to a relay contact l2a, and the heating elements 13b in the other pair of opposite blades 2. are connected to a relay contact I2b. Considering propeller l6, one pair of heating elements |3c are connected to a relay contact lie, and the other pair I3d are connected to a relay contact PM. The various pairs of heating elements of propellers l1 and I8 are similarly connected to relay contacts I 2e, I2}, I29, and 12h, respectively.

Each of the contacts l2 constitutes, together with an armature ll, parts of a relay II. All of the armatures i la to llh, inclusive, are connected to one terminal of a source 23 of heating current. The other terminal of the source 23 is grounded, so that closure of any armature H on its contact l2 completes a circuit to one pair of heating elements l3a or lib, et cetera.

The relays lta to Ith, inclusive, are adapted to be successively energized by a switching system, in accordance with the invention. This system includes a pair of wafer switches 3t and 31, each having a segment 35 in the case of switch 34, and 33 in the case of switch 31, which segment is constantly connected to a contact 35 or 33 and is adapted to successively make with each of four fixed contacts. In the case of switch 3'! these four fixed contacts are identified with the reference numerals B, D, F, and H, respectively, and in the case of switch 34 by the reference numerals A, C, E, and G, respectively. The segments 35 and 39 are connected to a common shaft 33 so that they move in synchronism with each other. The segments 35 and 33 are so oriented with respect to each other and their fixed contacts that each makes with a new fixed contact before the other breaks from its associated fixed contact. Thus in the position in which the switches are shown in Fig. 1, the segment 35 is shown closed on the contact A and the segment 39 is shown closed on the contact B. Segment 35 will leave contact A and close on contact C before segment 39 leaves contact B.

Each of the fixed contacts A to H inclusive of the switches 34 and 3! is connected directly to one terminal of the relay !9 bearing the corresponding sufiix letter, the other terminal of the relay being grounded. The segments 35 and 39 are constantly connected through the contacts 36 and 33 respectively, with contacts 322 and 324 of a cam-actuated switch 32. This switch has a leaf spring 325 which is adapted to either connect the contact 322 with a contact 32! or connect the contact 324 with a contact 323. The contacts 32! and 323 are connected to one terminal of a current source 33, the other terminal of which is grounded, so that although the two wafer switches 34 and 3'! may simultaneously complete circuits from the switch 32 to more than one of the relays !9a to llh, inclusive, the switch 32 functions to energize only one of those relays at atime' The switch 32 is of the snap-action type disclosed in Figs. 3 and 4. It comprises a casing 339 having the four fixed contacts 32!, 322, 323, and 324 anchored in opposite walls of the casing, and two movable contacts 325, 325 on opposite ends of the leaf spring 325. The spring 325 floats in the casing, being guided by ribs 33! on the front and rear walls of the casing. The spring 325 has slots cut therein to form two tongues 32! which extend inwardly toward each other from opposite ends of the spring into engagement with a U shaped clip 332 on the plunger 323, the latter being guided by an opening '335 in the front wall of the casing 339 through which it projects. The

plunger 329 also has a stem 335 which extends through a central recess 338 in the spring 325 and through an opening 339 in the rear wall of the casing 339. I

When the plunger 323 is unrestrained by any external force, as shown in Fig. 3, the tongues 32! are bowed upwardly. holding the'contacts 325, 325 against the stationary contacts 323 and 324, respectively, and closing-a circuit therebetween. When the plunger323 is pressed inwardly, the ends of the tongues 32'! are bent down wardly until they pass the mid-point of the spring 325, whereupon they snap into a reverse bowed position in which the contacts 326, 326 are snapped away from the stationary contacts 323 and 324, and into contact with the stationary contacts 32! and 322. When the plunger 328 is released, a helical compression spring 329 forces the stem 335 and the plunger, 329 into the normal position shown in Fig. 3. Y Referring back to Fi 1, the plunger 328 of the switch 32 is: actuated by a cam 3! on a shaft 29 which is geared to the shaft 39. Thus the shaft 39 has a large spur gear 23 meshing with a smaller spur gear 2'! on the shaft 29. To drive the entire switching mechanism, a worm wheel 25 is also provided on the shaft 29 which meshes with a worm 25 on the shaft of the drivin motor 24.

The speed of-rotation of the shaft 29 depends upon the length of time that the heating current is to be applied to each pair ofopposite heating elements l3, l3 of the propellers and can be regulated by properly choosing the speed of the motor 24 and the speed reduction produced by the worm 25 and the worm wheel 25.

However, the ratio of the speed of the shaft 39 to the shaft 29 is one to four, and the cam 3! is so shaped that it reverses the switch 32 at the end of each half revolution.

Th phasing of the cam 3! with respect to the segments and 39 is such that the switch 32' is reversed before one segment breaks from one of its associated four fixed contacts, but after the other segment has made with a new one of its four fixed contacts.

Thus as shown in Fig. 1, current flows from the source 33 through the upper contacts 32! and 322 of the switch 32, through the contact 35 and the segment 35 to the fixed contact A, and thencenver a conductor !9a to the relay, l9a, energizing the latter to close its armature !'!a on its contact I24: and energizethe heating elements !3a, !3a of propeller I5. The circuit is shown in position just before the cam 3! reverses the switch 32. It will be observed that although segment 35 is still contacting the fixed contact A, it is just about to leave it. Furthermore, the segment 39 has just made contact with the fixed contact B. Therefore, at the instant the switch 32 reverses, it cuts current off the relay !9a and almost simultaneously applies it over the contacts 323 and 324 of switch 32, th contact 33, segment 39, and contact B of switch 31, and over a lead [912 to the relay I9b, energizing the latter to close its armature llb on its contact I21; and energize the heating elements l3b, !3b of propeller l5.

It is important to note that the relative timing of the breaking of the circuit to relay !9a, and the making of the circuit to relay !9b is determined by the switch 32 and not by the wafer switches 34 and 31. In practice, snap action switches, such as the switch 32, switch so rapidly from one pair of contacts to the other that the interruption in current flow is extremely short, thereby permitting maximum use of the available heating current, without danger of overloading the current source by simultaneously energizing two of the relays l9.

The switching action described repeats itself to successively close the circuit from the source 33 to the relays l9c, l9d, I96, f, Mg, and !9h. Thus when the segment 39 is just about to leave the fixed contact B, the segment 35 will have left the contact A and closed on the contact C, so that the next reversal of the switch 32 back into the position shown in Fig. 1 will apply current over the fixed contact C and the lead l9c to the relay !9c.

The timing of the energizations of the diiferent relays !9a to IM inclusive is illustrated by the upper line 59 of Fig. 5, in which the period of energization of each of the relays is indicated by one of the segments 59a to 59h inclusive. The line 59 is divided into four equal parts by the vertical lines 5!, the distance between successive vertical lines representing the time required for one quarter revolution of the shaft 30 and one revolution'of the shaft 29. It will be noted that the cam 3| reverses the switch 32 at the end of each half revolution, thereby applying current successively to the eight different relays a to I07: during each complete cycle (represented by one complete revolution of the shaft 30). J l

The lines 50a, 50b, et cetera, are ofequal length because the cam 3| is shaped to actuate the switch-32 at 180 intervals. Obviously, if unequal heating periods in successive circuits is desired, the cam 3i would be shaped to successively actuate the switch at angular intervals that are unequal, but the sum of which is 360.

With four-blade propellers it is feasible to energize the heating elements in only half the blades at a time because the two blades of each pair are diametrically opposite and are in balanced relation. It is not desirable to de-ice one blade without simultaneously de-icing the opposite blade, because of vibration resulting from unbalance. Therefore where three-blade propellers are involved, it is the usual practice to apply-the heating current to the heating elements in all three blades simultaneously. Hence on an airplane having four 3-blade propellers, the switching system must successively concentrate all of the heating current in all the blades of successive propellers. This requires a switch having a four position cycle instead of an eight position cycle. Thus heating current would be applied to each circuit for 25% of the cycle instead of 12 as in the case with the timer shown in Fig. 1. If current is required for a shorter portion of the cycle it is still desirable to make certain that heating current is applied to each propeller for equal periods of time. This requirement can be met with only the one wafer switch 31 instead of the two wafer switches 34 and 31 as described in connection with Fig. 1.

Thus, in Fig. 2 the four fixed contacts B, D, F, and H of switch 31 are connected by the leads l9b, I311, l9f, and [971 to four relays lob, Hid, l0), and I 0h, each of which functions when energized to close an armature II on a contact i2 and connect the source 23 simultaneously to all three heating elements I4 01' the associated propeller 30, SI, 62, or 63 asthe case may be.

As in the system of Fig. 1, the segment 39 is of such arcuate length that it breaks from one of the contacts B, D, F, or H before it makes with the next one. Since the switch 34 of Fig. 1 is omitted in the system of Fig. 2, the contacts 32l and 322 of the switch 32 perform no function and could be omitted. It-is only when the switch 32 is in position to interconnect its contacts 323 and 324 that current flows from the source 33.

In the operation of the system shown in Fig. 2 the switch 32 is in the position shown, in which its contacts 323 and 324 are interconnected, shortly after the segment 33 has contacted one of the fixed contacts B, D, F, or H. As in the system of Fig. 1, the switch 32 serves to make and break the circuit, thereby relieving the segment 39 of this function and preventing arcing and burning.

Referring to Fig. 5, the interrupted line 52 shows the time during which circuits are completed over the four contacts .8, D, F, and B, re-

spectively. It will be observed that each circuit is completed an equal portion of a quarter cycle.

The shape of cam 50 determines the length of time current is applied to each propeller circuit. With the cam shown, the circuit from contact 38 through segment 39 to contact B is. made for approximately 75% of each revolution of shaft 29. At the time cam 50 operates switch 32 to break the circuit between contacts 323 and 324, segment 39 is about to leave contact B. Segment 39 leaves contact D during the portion of the cycle that cam 50 has opened the circuit between contacts 323 and 324, thus preventing any arcing on the wafer switch.

Although for the purpose of explaining the invention, a particular embodiment thereof has been shown and described, obvious modifications will occur to a person skilled in the art, and I do not desire to be limited to the exact details shown and described.

I claim:

A distributor of the type described for sue cessively applying a continuous potential from a common source to a plurality of circiuts in predetermined sequence comprising: first and second switches, each having a master terminal and a plurality of branch terminals and having means for successively switching its master terminal from one branch terminal to another. successive branch terminals of each switch being connected to alternate circuits in said sequence; means driving said first and second switches in synchronism with each other and in such phase relation that'their respective master terminals are alternately switched to diflerent branch terminals; a double-throw snap-action switch and means for reversing it between its two positions in timed relation with said first and second switches, said double-throw switch continuously connecting said source to the master terminal of said first switch in one position and to the master terminal of said second switch in the other position; each of said first and second switches connecting its master terminal to each branch terminal for an interval of time exceeding the interval between successive reversals of said doublethrow switch and being so phased with respect to the double-throw switch that it maintains its master terminal connected to a single branch terminal throughout the interval between successive reversals of said double-throw switch from one position to the other, whereby said source is progressively connected to successive ones of said circuits in said sequence, said double-throw switch, by virtue of its snap action, reversing at a speed independent of the speed of said driving means, and substantially instantaneously, whereby interruption of current fiow from said source to said said circuits is minimized.

ROBERT G. HOOF.

REFERENCES CITED The following references file of this patent:

UNITED STATES PATENTS are of record in the. 

